German published patent application 34 13 739 discloses a power booster of this kind. The special features of the known power booster include, in order to eliminate the suction noises caused on actuation by the inflowing air, an air-conducting element which is held by the actuating rod and projects into the interior of the poppet valve member. The element has radially outwardly extending conducting surfaces which are designed as flanges, grooves, ribs, or vanes. In the area of its sealing surface cooperating with the first sealing seat designed on the control housing, the poppet valve member has a cylindrical projection extending towards the valve piston and cooperating with the wall in the control housing that confines the first sealing seat; the projection prevents the end of the poppet valve member on the side of the valve piston from moving in a radial direction.
A disadvantage in the known power booster is the complicated design of the poppet valve member which is required for the desired deflection of the inflowing air, in particular in the area of the first sealing seat. The problematic assembly of the air-conducting element is also undesirable. When assembling the booster, an angular clearance at the actuating rod of roughly .+-.3.degree. must be ensured, due to the kinematics of actuation, so that an annular gap must be maintained between the air-conducting element and the actuating rod. Consequently, the desired effect is impaired.
Another shortcoming is in the vertically arranged flange of the air-conducting element, which may reflect the striking air flow and cause turbulences and sound reflection.